Tubing having openings therein for delivery of stimulation fluids such as, for example, steam to, and for receiving fluids from, a formation are known. Often the openings have removable closures for use during tubing installation. Once the closures are removed, the openings are permanently open.
Recently, a tubing assembly including a sliding sleeve valve has been used in controlling stimulation fluid flow into formations. The tubing assembly includes a sliding sleeve valve positioned over a port through the tubing wall. The sliding sleeve valve is moveable between a closed position, wherein the sleeve blocks the port, and an open position for permitting the flow of the stimulation fluid through the port and to the formation.
Various problems have been encountered by use of the previous sliding sleeve valve tubing assembly. In particular, the stimulation fluid passing through the port tends to cause damage to the formation because of the high pressures of the fluid. In addition, when the sleeve is maintained in the closed position for extended periods, it tends to jam due to a pressure lock and the port tends to become blocked with scale or debris.
The sliding sleeve valves are sometimes used in series along a tubing string in a well. It is intended that the provision of a series of valves will permit stimulation fluid to be delivered along a length of the well. However, it often occurs that the stimulation fluid passes out through the first few valves that it reaches so that the deeper valves transport very little or no stimulation fluid to the formation.